The invention discloses a rotary mud blowout preventer for a well mouth. The rotary mud blowout preventer comprises a substrate assembly, and a first telescopic boom, a second telescopic boom and a third telescopic boom mutually connected in a sleeving manner, wherein a rotary liquid cylinder is installed between the substrate assembly and the first telescopic boom, the top end of the third telescopic boom is connected with one end of an opening-closing stand column via a bolt, the other end of the opening-closing stand column is connected with a mud barrel, opening-closing hydraulic cylinders are symmetrically installed on two sides of the outer wall of the mud barrel, the bottom of the side wall of the mud barrel is connected with one end of a mud recycling assembly, and the other end of the mud recycling assembly is installed on the substrate assembly via a flange. According to the rotary mud blowout preventer for the well mouth provided by the invention, pollution to environment caused by spraying of residual mud in a drilling tool is effectively avoided, no mud remains in the drilling tool, and all mud is recycled, so that production cost is saved; the rotary mud blowout preventer is compact in structure and small in occupied area, without influencing the layout of a drilling floor; according to the rotary mud blowout preventer, remote, automatic and full-hydraulic control on the mud remained in the drilling tool is achieved, and thus the preventer is time-saving and labor-saving.